Threaded electrical connections

ABSTRACT

Electrical terminal device comprises tubular member having axially extending seam which is flared at one end to facilitate wire entry. Internal surface is threaded so that threads are cut into surface of wire when terminal is threaded onto wire end. An axially extending slot may be provided which extends partially along the tubular member from the flared end to permit radial expansion when the tubular member is threaded onto a wire.

Ullltd States Patent [191 Aldridge s41 THREADED ELECTRICAL CONNECTIONS [75 Inventor: Lionel Dennis Aldridge, Seminole,

Fla.

[7 3] Assignee: AMP Incorporated, Harrisburg, Pa. [22] Filed: Jan. 8, 1971 [21] .Appl. No.: 104,944

[52] 11.8. CI. ..339/95 R, 174/84 [51] Int. Cl. ..Ii0lr 11/20 [58] Field of Search ....339/95, 213, 276; 174/84, 87,

, [56] References Cited UNITED STATES PATENTS 2,371,469 3/1945 Rogoft "339/276 T 1,700,985 2/1929 Jasper ..174/87 2,434,475 7 1/1948 Sullivan ..339/95 B 51 Feb. 20, 1973 FOREIGN PATENTS OR APPLICATIONS 1/1957 GreatBritain ..339/276T 7/1948 Netherlands ..l74/87 Primary Examiner-Joseph H. McGlynn Attorney-William J. Keating, Ronald D. Grefe Gerald K. Kita, Frederick W. Raring, Jay L. Seitchik, John R. Flanagan and Allan B. Osborne [5 7] ABSTRACT Electrical terminal device comprises tubular member having axially extending seam which is flared at one end to facilitate wire entry. Internal surface is threaded so that threads are cut into surface of wire when terminal is threaded onto wire end. An axially extending slot may be provided which extends partially along the tubular member from the flared end to permit radial expansion when the tubular member is threaded onto a wire.

' 7 Claims, 8 Drawing Figures THREADED ELECTRICAL CONNECTIONS BACKGROUND OF THE INVENTION This invention relates to terminal devices of the type which can be directly applied to a wire without the use of special tools. The invention is herein disclosed in an embodiment adapted for use with aluminum wires although the principles of the invention can be applied to terminals intended wires of other metals.

Aluminum wire is being used to an increasing extent for domestic wiring for buildings in place of conventional copper wire because of the relatively low cost of aluminum and the fact that it is an excellent conductor of electricity. The use of aluminum, however, presents several problems which are not encountered with copper wires which have retarded more widespread use. One problem encountered is that a hard, thin oxide is formed on aluminum wires which interferes with the achievement of good electrical contact. This oxide can be removed by scraping or abrasion but it will reform in a short time if the electrical interface is exposed to the atmosphere. It follows that when a terminal is applied to. an aluminum wire, the oxide must be removed immediately before application and the termination must be such that access of air to the terminal-wire interface is prevented.

A further problem encountered is that aluminum, to an extent greater than copper, has a tendency to cold flow or creep at room temperature or at slightly elevated temperatures under the influence of relatively low stresses. Creep can result in a relaxation of an electrical connectionwith resulting loss in contact pressure and/or the formation of cracks or openings at the electrical interface which permit the entry of oxygen with the resulting formation of an oxide coating on the aluminum wire. Both relaxation and oxide formation result in degradation of the electrical connection.

a A still further problem which is encountered with aluminum wires is that aluminum is anodic to most other metals and galvanic corrosion will result when an aluminum part, such as a wire, is located adjacent to a part such as a terminal which is higher on the electromotive series than aluminum. Galvanic corrosion ean thus destroy or degrade an aluminum wire connection within a comparatively short time.

The instant invention is directed to the achievement of an improved terminating device which can be manually applied to a wire end, which, during application, forms fresh oxide-free surface on the wire end, and which upon-application is resiliently stressed in a manner such that portions of the terminal are urged against surface portions of the wire to maintain an unrelenting contact pressure.

It is accordingly an object-of the invention to provide an improved terminal device. A further object is to provide a terminal device which can be used on an aluminum wire. A further object is to provide a terminal briefly described in the foregoing abstract, which is described in detail below, and which is shown in the accompanying drawings in which:

FIG. 1 is a perspective view of a preferred form of terminal in accordance with the invention.

FIG. 2 is a perspective view, partially in section, of the opposite side of the terminal from the side shown in FIG. 1.

FIG. 3 is a plan view of the blank from which the terminal of FIG. 1 is formed.

FIG. 4 is a sectional side view of the terminal of FIG. 1 showing the position of a wire during the initial stage of application of the terminal to the wire.

FIG. 5 is a view similar to FIG. 4 but showing the wire as fully inserted into the terminal.

FIGS. 6 and 7 are views taken along the lines 6-6 and 7-7 of FIG. 4.

FIG. 8 is a side view of the terminal of FIG. 1.

A terminal 2 in accordance with the invention comprises a generally cylindrical barrel 4 having an axially extending seam 8 having edges 9, 11, which is preferably not brazed or otherwise bonded but which is substantially closed throughout most of the length of the barrel. It will be apparent from FIGS. 2 and 7 that the open seam is formed by an axially extending edge 'which is opposed to, and substantially against, the internal surface of barrel 4. The righthand end of the barrel portion as viewed in FIGS. 2 and 4 is flared outwardly as shown at 10 to facilitate entry of the wire and the edges 9, ll of the seam are divergent at this end of the terminal barrel. Screw threads 16 are provided on the internal surface of the barrel for the full length thereof and an axially extending slot 14 extends forwardly from the rearward end 10 partially along the length of the barrel and past the flared portion.

The forward end 6 of the terminal 2 has contact means in the form of a ring tongue 20 which is connected to the barrel 4 by a transition section 18 which appears to be generally triangular when viewed from above. One side of this transition section is integral with the lower edge of the barrel and the seam 8 which extends along this transition section is tightly closed as shown. a l I A preferred material for the manufacture of .terminal devices in accordance with the invention is a low carbon steel which has been plated with tin or zinc. Low carbon steel is relatively close to aluminum in the electromotive series so that corrosion issminimized and further protection against corrosion can be obtained by tin plating or by plating with a sacrificial metal such as zinc. A low carbon steel is alsoadvantageous in that it has good spring properties which are needed as described below.

The terminal of 2' is preferably manufactured by merely forming, in a progressive die, a blank 2', FIG. 3, upon which the screw threads have been impressed by coining. The coining operation produces some localized hardening on the surface of the blank so that the resulting screw threads will'be sufficiently hard to cut into the wire when the terminal is applied. The threads are advantageously relatively coarse, for example, 'a 4/32 thread being well suited for a terminal adapted to be used on an AWG 10 wire. The stock metal from which the terminal is formed should have a thickness sufficient to develop the required spring properties for the terminal; for example, a 0.046 inch thick low carbon steel stock is advantageous for a terminal intended for use with a AWG wire.

When the terminal 2 is applied to the end 22 of a wire, the insulation on the wire is removed from the wire end and the wire and the terminal are positioned in alignment with each other with the end of a wire extended into the flared rearward end of the terminal. The terminal is then turned or rotated onto the wire until the wire end is located at or adjacent to the lefthand end of the barrel 4. During each rotation of the barrel relative to the wire, the edges of the threads adjacent to the open end of the seam and the' edge of the slot 14 cut into the surface of the wire and form threads 24 on the wire surface to an increasing depth until male threads are formed which conform to the female threads in the barrel. Thread formation on the wire end may take place as a result of flow of the metal on the wire surface without removal of material or by cutting of the wire. By either method, fresh surface will be formed on the wire which will be free of the characteristic oxide on an aluminum surface and this fresh surface will be maintained in tight contact with the internal surface of the barrel. If chips are produced, as shown in FIG. 6, they will be ejected through the slot 14. It follows that a high quality electrical connection is achieved since the fresh aluminum surface is not permitted to oxidize during the brief interval between thread formation on the wire and final movement of the wire into the barrel.

The primary purpose of the slot 14 is to permit the end portion 10 of the barrel to be flexed outwardly when the wire is started into the barrel although the slot also permits ship removal as noted above. It should be mentioned that more than one slot may be provided or the slot 14 need not be provided at all, particularly if the terminal is intended for use on a relatively finer gage wire where little force is required to start the wire into the barrel.

The internal diameter of the barrel is advantageously such that the barrel will be circumferentially stressed during application and the seam 8 will beopened slightly'from the position shown in FIG. 2. The stresses imposed, however, are within the elastic limit of the material of the barrel and the seam, therefore, has a tendency to close. The internal threads in the barrel are thus pressed firmly against'the wire end, and should the wire relax or creep, the barrel will follow the wire to maintain intimate physical and electrical contact. It should be noted that the threads 24 of the disclosed embodiment'are righthand threads and that turning of the terminal onto the wire will tend to open the seam, against its inherent. tendency to remain closed, and resiliently stress thev barrel in 'a manner such that it tends to close itself onto the wire and maintain the contact pressure. vIf the seam were on theopposite side of the barrel from the side shown, lefthand threads would .be formed in the barrel to achieve the same result. In other words, the sense (righthand or lefthand) of the threads is opposite to the sense in which the barrel extends from the edge 9 to the edge 11 when the barrel is viewed from its rearward end.

The location of the seams 8 along the side of the barrel is advantageous in that the amount of energy which can be stored in the barrel is maximized because of the fact that almost the entire circumference of the barrel is flexed.

Obvious modifications within the scope of the appended claims will be apparent to those skilled in the terminal art. For example, insulating sleeve can be applied to the wire end if desired by shrinking the sleeve into the barrel. A wide variety of contact types can be providedon the terminal, the disclosed form of ring tongue constitutes one commonly used type. The particular arrangement shown has the advantage of locating the ring tongue only slightly off center with respect to the access of the barrel.

While a mild steel is a preferred material, as noted above, terminals in accordance with the invention can also be manufactured from other metals such as spring temper brass or aluminum alloy 6061.

What is claimed is:

1. An electrical connecting device comprising a rolled tubular member having an axially extending open seam, said seam being defined by one axially extending edge of said member which is opposed to, and substantially, against the internal surface of said member,

said member having a wire-receiving end, at least one axial slot extending from said wire-receiving end partially along the length of said member, and

screw threads on the internal surface of said member, said threads extending in the same direction as said tubular member extends circumferentially from said one edge aroundthe circumference of said member whereby, upon threading said tubular member onto one end of a wire, portions of said threads adjacent to the edges of said slot engage said wire and, as threading of said member onto said wire continues, threads are formed on said wire, and said tubular member is resiliently circumferentially stressed in the direction which tends to open said seam and said threads in said tubular member are maintained in engagement with the threads formed in said wire.

2. An electrical connecting device as set forth in claim 1 wherein said wire-receiving end is flaired outwardly to facilitate entry of said wire.

3. A device for forming an electrical connection to wire comprising:

a tubular member of resilient conductive metal having an'axially extending seam,

a contact portion at one end of said tubular member, said contact portion being integral with one edge of said seam and lying in a plane which extends substantially tangentially with respect to said tubular member, and

screw threads on the internal surface of said tubular member, said threads extending in said tubular member in the same direction as said barrel extends from said one edge to the second edge of said tubular member whereby, upon threading said tubular member onto a wire, threads are formed on the surface of said wire and said seam tends to be' opened by said wire whereby said barrel is resiliently urged against said wire.

4. A device as set forth in claim 3 wherein said tubular member is outwardly flared at the end thereof which is opposite to said one end.

5. A device as set forth in claim 3 wherein said tubular member has a slot extending inwardly from the end which is opposite to said one end.

6. A device as set forth in claim 3 wherein the sense of said screw threads is opposite to the sense in which said barrel extends from said one edge to the other edge of said barrel.

7. A device for forming an electrical connection to a wire comprising:

a tubular member of resilient conductive metal having an axially extending seam, a contact portion integral with, and extending from, one edge of said seam proximate to one end of said tubular member, said contact portion extending substantially tangentially with respect to said tubular member,

screw threads on the internal surface of said tubular member, said screw threads extending, from the end opposite to said one end, in the sense which is opposite to the sense in which said tubular portion 5 extends from said one edge of said seam to the other edge of said seam when said tubular portion is viewed from said opposite end whereby, upon threading said tubular member onto a wire, said threads form complementary threads on said wire, and 10 said tubular member is resiliently stressed in the sense of said threads and is resiliently maintained in engagement with said wire. 

1. An electrical connecting device comprising a rolled tubular member havinG an axially extending open seam, said seam being defined by one axially extending edge of said member which is opposed to, and substantially, against the internal surface of said member, said member having a wire-receiving end, at least one axial slot extending from said wire-receiving end partially along the length of said member, and screw threads on the internal surface of said member, said threads extending in the same direction as said tubular member extends circumferentially from said one edge around the circumference of said member whereby, upon threading said tubular member onto one end of a wire, portions of said threads adjacent to the edges of said slot engage said wire and, as threading of said member onto said wire continues, threads are formed on said wire, and said tubular member is resiliently circumferentially stressed in the direction which tends to open said seam and said threads in said tubular member are maintained in engagement with the threads formed in said wire.
 1. An electrical connecting device comprising a rolled tubular member havinG an axially extending open seam, said seam being defined by one axially extending edge of said member which is opposed to, and substantially, against the internal surface of said member, said member having a wire-receiving end, at least one axial slot extending from said wire-receiving end partially along the length of said member, and screw threads on the internal surface of said member, said threads extending in the same direction as said tubular member extends circumferentially from said one edge around the circumference of said member whereby, upon threading said tubular member onto one end of a wire, portions of said threads adjacent to the edges of said slot engage said wire and, as threading of said member onto said wire continues, threads are formed on said wire, and said tubular member is resiliently circumferentially stressed in the direction which tends to open said seam and said threads in said tubular member are maintained in engagement with the threads formed in said wire.
 2. An electrical connecting device as set forth in claim 1 wherein said wire-receiving end is flaired outwardly to facilitate entry of said wire.
 3. A device for forming an electrical connection to a wire comprising: a tubular member of resilient conductive metal having an axially extending seam, a contact portion at one end of said tubular member, said contact portion being integral with one edge of said seam and lying in a plane which extends substantially tangentially with respect to said tubular member, and screw threads on the internal surface of said tubular member, said threads extending in said tubular member in the same direction as said barrel extends from said one edge to the second edge of said tubular member whereby, upon threading said tubular member onto a wire, threads are formed on the surface of said wire and said seam tends to be opened by said wire whereby said barrel is resiliently urged against said wire.
 4. A device as set forth in claim 3 wherein said tubular member is outwardly flared at the end thereof which is opposite to said one end.
 5. A device as set forth in claim 3 wherein said tubular member has a slot extending inwardly from the end which is opposite to said one end.
 6. A device as set forth in claim 3 wherein the sense of said screw threads is opposite to the sense in which said barrel extends from said one edge to the other edge of said barrel. 